Steam-heated and induction-heated rollers are used in the paper making, printing, paper, film, and foil converting industries. Some examples are: web heating rollers, drying rollers and drums, laminating rollers, embossing rollers, and cast film extrusion rollers.
Steam-heated rollers are actually pressure vessels, especially at higher temperatures. The internal construction of both steam-heated and induction-heated cores can be quite complex and expensive in order to provide the temperature uniformity needed. In addition, a considerable amount of auxiliary equipment is needed to power or heat the roller.
Hyllberg, U.S. Pat. No. 5,616,263, issued Apr. 1, 1997 and U.S. Pat. No. 5,869,808, issued Feb. 9, 1999 disclose a ceramic heater roller for use in industrial applications. Hyllberg, U.S. Pat. No. 5,408,070, discloses a ceramic heater roller with a heater layer and a heat regulating layer. Hyllberg et al., U.S. Pat. No. 5,420,395, discloses a roller in which the ceramic layer is divided into zones for zone heating and wires are used inside the core to connect to the various ceramic heating sections.
There is a basic problem with heated rollers in controlling the heating at the ends of the roller. When the width of a web of paper or other material is smaller than the heated length of the roller, the ends of the roller operate at a higher temperature than the portion covered by the web of paper or other material, which tends to dissipate heat from the covered portion of the roller. The higher temperature at the roller ends causes heat to migrate through the core and into the web area increasing temperature variation across the web. Also, the higher temperature at the ends can accelerate aging of an outer covering, where the outer covering is rubber, for example.
Heat pipe technology has been used to control heat in various kinds of equipment used for space exploration, remote monitoring stations and wherever heat transfer is required. A basic industrial heat pipe roller is disclosed in Noren, U.S. Pat. No. 3,700,028. As reported in Noren, "How Heat Pipes Work," Chemical Engineering, Aug. 19, 1974, acceptance of heat pipes in industry has been slow. Since that time a number of heat pipe constructions have been patented, often for small rollers used in office copiers and printers. Progress has remained slow, however, for industrial and large equipment applications.
The present invention is directed to a heater roller that controls temperature along the length and around the working surface of a cylindrical roller. This roller is advantageous for manufacture and overcomes many of the typical problems cited in the prior art.